The present invention relates to methods and apparatuses for orienting a cutting tool. More particularly, the present invention relates to methods and apparatuses for controlling, reducing or eliminating the tapered edge that results when a workpiece is cut with a cutting tool.
Cutting tools for cutting workpieces are generally known, with examples including drills and the like. One particular genre of cutting tools is non-contact cutting tools. Typically these tools emit a high energy stream towards a workpiece to cut the workpiece. Examples of such non-contact cutting tools include laser tools, torches such as an acetylene torch, plasma cutting tools, and high pressure waterjets.
Taking waterjet systems as exemplary of non-contact cutting tools, a typical waterjet system includes a waterjet head that is supplied with liquid at an ultra high pressure (UHP), for example 10,000 to 60,000 pounds per square inch (psi). The UHP liquid is discharged in an axial direction from the head in a high velocity stream against the workpiece. The liquid stream is used to cut through materials such as wood, metal, paper and foam. An abrasive particulate material can be added to the stream, and the liquid/abrasive stream can be used to cut through composites, metals and other dense materials. The cutting stream typically is concentrated in a small area that may be for example about 0.05 inch diameter, and has a high flow rate of for example about one to three gallons per minute (gpm). With commonly available equipment, the waterjet head and the cutting stream are maintained perpendicular to the top surface of the workpiece and are moved by a computer numerically controlled (CNC) system in order to cut through the workpiece along a cut line.
Although non-contact cutting tools such as waterjet systems have many advantages, an unfortunate result of making a cut with such a tool can be the taper of the cut edge. In most instances it would be desirable for the finished edge to have no taper and to be in a plane perpendicular to the workpiece top surface. However, the non-contact cutting stream, such as the water stream, may produce an edge that is inclined or tapered. The cutting stream may remove more material at the top than at the bottom of the cut, and in this case the resulting cut edge has what can be termed a positive taper. Referring particularly to waterjet systems by way of example, the amount of the taper is dependent on many variables including the speed at which the waterjet head is moved along the workpiece surface. At very slow speeds a relatively taper-free or a negatively tapered edge can be formed. Slower cutting speeds, however, increase production times and are disadvantageous.
A prior art waterjet cutting system designated as a whole as 10 is shown in FIG. 1. The system 10 is used to form a cut 12 in a workpiece 14, and includes a waterjet head assembly 16. The waterjet head 16 includes a valve body 18 operated to open or closed positions by an actuator 20 controlled remotely by the presence or absence of pressurized air supplied to the actuator 20 through an air control conduit 22. Ultra high pressure (UHP) liquid is supplied to the waterjet head 16 from a suitable UHP pump system 21 at pressures of between about 10,000 and 60,000 PSIG through a UHP liquid supply conduit 23 normally formed of stainless steel and having sufficient flexibility to permit movement of the waterjet head 16 around the surface of the workpiece 14.
A valve nut 24 attaches a tube 26 to the bottom of the valve body 18. When the valve in the valve body 18 is opened by the application of pressurized air within the actuator 20, UHP liquid flows downward through the valve body 18 and the tube 26 to an outlet nozzle assembly 28 including a mixing chamber housing 30 and a nozzle 32. The nozzle 32 is aligned with the longitudinal axis of the waterjet head 16, and includes an axial discharge passage through which a concentrated UHP liquid stream is discharged at high pressure and high velocity.
For many applications, fine particles of an abrasive material such as garnet are added to the liquid stream. The mixing chamber member 30 receives particulate abrasive through a flexible rubber or neoprene abrasive supply line 34. When UHP liquid flows through the mixing chamber member 30, abrasive material is entranced in the liquid stream and a liquid/abrasive stream having increased cutting capability is discharged from the nozzle 32.
The waterjet head 16 is supported, typically with its axis vertical and perpendicular to the top surface 38 of the workpiece 14, by a clamp 36 or similar fixture. The clamp 36 is carried by a support arm 40 extending from a clamp plate 42 attached to a front plate 44 of a support member or lift 46. The lift 46 is moved in three orthogonal directions by a three axis X-Y-Z drive 48. Typically the drive 48 can move the waterjet head 16 in an X direction from side to side over the workpiece 14 and, separately or simultaneously, in a Y direction forward and rearward over the workpiece 14. The drive 48 can also move the head 16 in a Z direction, vertically with respect to the workpiece. A computer numerical control (CNC) system 50 controls the drive 48 to perform a cutting operation upon the workpiece 14. The head is moved in the Z direction to place the outlet of the nozzle 32 near the top workpiece surface 38. Then the control system moves the head 16 in the X and/or Y directions to form the cut 12. Typically the control system 50 is programmed to cut the workpiece in selected straight and/or curved lines and/or corners to fabricate finished parts having a desired shape.
Prior art waterjet systems of the type seen in FIG. 1 are commercially available from sources including EASE Cutting Systems, 411 Ebenezer Road, Florence, S.C. 29501-0504. A further description of the prior art system 10 can be found at the title pages and pages 2-4, 2-5, 2-7, 2-8, 2-12, 4-29, 4-30 and 2-24 through 6-26 of ESAB Cutting Systems manual No. F14-135 dated May, 1999, filed herewith and incorporated herein by reference. A further description of a prior art waterjet head can also be found in U.S. Pat. No. 6,126,524 incorporated herein by reference.
When the cut 12 is formed in the workpiece 14 by the vertically disposed head 16, the sides of the cut 12 are defined by inclined, sloped walls 12A and 12B. These sloped walls form a tapered cut 12. The slope of the sides 12A and 12B of the tapered cut 12 can be as large as a several degrees. This taper can be undesirable, and in most operations a sidewall of the finished part that is perpendicular to the top surface 38 would be preferred. In some operations, a taper different from that of sides 12A and 12B would be preferred, for example to provide a beveled edge.
It would be desirable to control the taper of the cut edge so that taper could be reduced or eliminated or, alternatively, so that a controlled beveled edge of a desired angle could be produced. It has been recognized that positive taper can be reduced by slowing the cutting speed of the waterjet head. This practice, however, adds to manufacturing time and cost. In addition, expensive five-axis tilt control assembly systems are available for providing tilt and rotation in addition to X-Y-and Z movement that may offer some degree of taper control. Known five axis systems, however, are costly, complex, and bulky. These and other factors are deterrents to their use.
A proposed solution for cut edge bevel control is shown in U.S. Pat. No. 5,199,342 to Hediger (xe2x80x9cthe ""342 patentxe2x80x9d). The system disclosed in the ""342 patent generally discloses a waterjet nozzle movably held by an X-Y drive system at a first point, and with the nozzle end pivotably held. X-Y movement at the first point causes the nozzle to be oriented at an angle to a workpiece. The X-Y drive system moves the first connection point in a first frame, which is movably held on a second frame. While some degree of tilt is provided, the overall configuration of the system of the ""342 patent entails a degree of complexity and cost that is undesirable.
Unresolved needs therefore remain in the art.
The present invention is directed to methods and apparatuses for controlling the taper of a workpiece edge cut by a cutting tool. A tilt control assembly of the invention includes a tilt control assembly body with first and second supports coupled to the body. Each of the first and second supports is connected to the head along an axis of the head. In a first exemplary tilt control assembly of the invention, the first support is eccentric and movably coupled to the tilt control assembly body. A drive is coupled to the first support and is operative to rotate the first head support and position the head at a selected angle to the workpiece. In a second exemplary tilt control assembly of the invention, both of the first and second supports are movable, and are coupled to a drive operative to rotate the first and second head supports and position the head at a selected angle to the workpiece. In a preferred embodiment of the apparatus of invention, both the first and second head supports are eccentric.
In still an additional aspect of the present invention, a method for positioning a cutting tool head is provided. An exemplary method comprises the steps of supporting a cutting tool head with first and second supports along an axis of the head, and moving both of the supports to position the head at a selected angle to the workpiece. Preferably, both the first and second supports are moved eccentrically.
Methods and apparatuses of the invention thereby provide advantages and solutions to problems of the prior art. For example, an apparatus of the invention that has two eccentric head supports provides compact and relatively inexpensive tilt control capabilities that can be used to control the taper of a cut edge over a wide range of taper or bevel angles. Additional advantages and aspects of the invention will be better understood through consideration of the detailed description of invention embodiments provided herein below.